[PATCH v2] zImage-arm: get rid of static offset

[PATCH v2] zImage-arm: get rid of static offset

[Daniel Mack]

The code in arch/arm/kexec-zImage-arm.c currently enforces a hard limit
on the maximum size a dtb blob can occupy. This limit is set to 32k,
which is quite low for device tree blobs nowadays.

Get rid of this assumption, and calculate the added size dynamically.
For this, we need to slurp in the dtb file earlier in order to
determine its size, because the memory hole allocation for 'base'
takes this size into account.

For ATAGs, we keep the current value of 32k, which should in fact be
enough.

With this change in place, the 'DTB too large!' error message can go
away. Successfully tested on a AM335x board.

Signed-off-by: Daniel Mack <zonque@gmail.com>
[s.neumann@raumfeld.com: Fix ATAGs case]
Reported-and-tested-by: Sven Neumann <s.neumann@raumfeld.com>
---
v2 includes a fixup from Sven Neumann for ATAGs driven boards.
The patch is in tested on a larger number of machines by now.

 kexec/arch/arm/kexec-zImage-arm.c | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/kexec/arch/arm/kexec-zImage-arm.c b/kexec/arch/arm/kexec-zImage-arm.c
index bfbf290..220826e 100644
--- a/kexec/arch/arm/kexec-zImage-arm.c
+++ b/kexec/arch/arm/kexec-zImage-arm.c
@@ -282,7 +282,7 @@ int zImage_arm_load(int argc, char **argv, const char *buf, off_t len,
 {
 	unsigned long base;
 	unsigned int atag_offset = 0x1000; /* 4k offset from memory start */
-	unsigned int offset = 0x8000;      /* 32k offset from memory start */
+	unsigned int extra_size = 0;
 	const char *command_line;
 	char *modified_cmdline = NULL;
 	off_t command_line_len;
@@ -360,6 +360,13 @@ int zImage_arm_load(int argc, char **argv, const char *buf, off_t len,
 		ramdisk_buf = slurp_file(ramdisk, &initrd_size);
 	}
 
+	if (dtb_file) {
+		dtb_buf = slurp_file(dtb_file, &dtb_length);
+		extra_size = _ALIGN(dtb_length, getpagesize());
+	} else if (use_atags) {
+		extra_size = 0x8000;	/* 32k should be plenty for ATAGs */
+	}
+
 	/*
 	 * If we are loading a dump capture kernel, we need to update kernel
 	 * command line and also add some additional segments.
@@ -398,7 +405,8 @@ int zImage_arm_load(int argc, char **argv, const char *buf, off_t len,
 		}
 		base = start;
 	} else {
-		base = locate_hole(info,len+offset,0,0,ULONG_MAX,INT_MAX);
+		base = locate_hole(info, len + extra_size, 0, 0,
+				   ULONG_MAX, INT_MAX);
 	}
 
 	if (base == ULONG_MAX)
@@ -428,8 +436,6 @@ int zImage_arm_load(int argc, char **argv, const char *buf, off_t len,
 		 * Read a user-specified DTB file.
 		 */
 		if (dtb_file) {
-			dtb_buf = slurp_file(dtb_file, &dtb_length);
-
 			if (fdt_check_header(dtb_buf) != 0) {
 				fprintf(stderr, "Invalid FDT buffer.\n");
 				return -1;
@@ -452,11 +458,6 @@ int zImage_arm_load(int argc, char **argv, const char *buf, off_t len,
 			create_flatten_tree(&dtb_buf, &dtb_length, command_line);
 		}
 
-		if (base + atag_offset + dtb_length > base + offset) {
-			fprintf(stderr, "DTB too large!\n");
-			return -1;
-		}
-
 		if (ramdisk) {
 			add_segment(info, ramdisk_buf, initrd_size,
 			            initrd_base, initrd_size);
@@ -485,9 +486,9 @@ int zImage_arm_load(int argc, char **argv, const char *buf, off_t len,
 		            dtb_offset, dtb_length);
 	}
 
-	add_segment(info, buf, len, base + offset, len);
+	add_segment(info, buf, len, base + extra_size, len);
 
-	info->entry = (void*)base + offset;
+	info->entry = (void*)base + extra_size;
 
 	return 0;
 }
-- 
1.9.0


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Re: [PATCH v2] zImage-arm: get rid of static offset

[Simon Horman]

On Thu, May 01, 2014 at 12:42:05PM +0200, Daniel Mack wrote:
> The code in arch/arm/kexec-zImage-arm.c currently enforces a hard limit
> on the maximum size a dtb blob can occupy. This limit is set to 32k,
> which is quite low for device tree blobs nowadays.
> 
> Get rid of this assumption, and calculate the added size dynamically.
> For this, we need to slurp in the dtb file earlier in order to
> determine its size, because the memory hole allocation for 'base'
> takes this size into account.
> 
> For ATAGs, we keep the current value of 32k, which should in fact be
> enough.
> 
> With this change in place, the 'DTB too large!' error message can go
> away. Successfully tested on a AM335x board.
> 
> Signed-off-by: Daniel Mack <zonque@gmail.com>
> [s.neumann@raumfeld.com: Fix ATAGs case]
> Reported-and-tested-by: Sven Neumann <s.neumann@raumfeld.com>
> ---
> v2 includes a fixup from Sven Neumann for ATAGs driven boards.
> The patch is in tested on a larger number of machines by now.

Thanks, applied.

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Re: [PATCH v2] zImage-arm: get rid of static offset

[Wang Nan]

On 2014/5/2 10:11, Simon Horman wrote:
> On Thu, May 01, 2014 at 12:42:05PM +0200, Daniel Mack wrote:
>> The code in arch/arm/kexec-zImage-arm.c currently enforces a hard limit
>> on the maximum size a dtb blob can occupy. This limit is set to 32k,
>> which is quite low for device tree blobs nowadays.
>>
>> Get rid of this assumption, and calculate the added size dynamically.
>> For this, we need to slurp in the dtb file earlier in order to
>> determine its size, because the memory hole allocation for 'base'
>> takes this size into account.
>>
>> For ATAGs, we keep the current value of 32k, which should in fact be
>> enough.
>>
>> With this change in place, the 'DTB too large!' error message can go
>> away. Successfully tested on a AM335x board.
>>
>> Signed-off-by: Daniel Mack <zonque@gmail.com>
>> [s.neumann@raumfeld.com: Fix ATAGs case]
>> Reported-and-tested-by: Sven Neumann <s.neumann@raumfeld.com>
>> ---
>> v2 includes a fixup from Sven Neumann for ATAGs driven boards.
>> The patch is in tested on a larger number of machines by now.
> 
> Thanks, applied.
> 

After applying this patch, the second kernel on qemu never works. I have
posted a patch on it to solve this problem:

 [kexec-tools][PATCH] zImage-arm: bugfix: load kernel at TEXT_OFFSET

I think there must be some misunderstanding about "DTB too large!" problem.
DTB is pasted after initrd by kexec, not before the kernel. See following figures:

When using DTB:

|<--- TEXT_OFFSET (0x8000) ------->|
|<-- atags, DTB *is not here* ---->|<-- zImage -->|<-- initrd -->|<-- *DTB is here* -->|

When using ATAGS:

|<-- TEXT_OFFSET (0x8000) ->|
|<-- 0x1000 --|<-- atags -->|<-- zImage -->|<-- initrd -->|

It seems the original code is incorrect:

      if (base + atag_offset + dtb_length > base + offset) { // offset is TEXT_OFFSET
              fprintf(stderr, "DTB too large!\n");
              return -1;
      }

This code assumes dtb is loaded between atags_offset and zImage, can use only 28KiB memory,
same as atags. However, dtb is loaded after initrd, no upper limit is taken place, so simply
remove the above checking is enough. In my patch, I use locate_holes() to endure there is enough
space for initrd and dtb.

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